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UserspaceEmulator: Recognize xor/sub zeroing idioms and don't taint

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"xor reg,reg" or "sub reg,reg" both zero out the register, which means
we know for sure the result is 0. So mark the value as initialized,
and make sure we don't taint the CPU flags.

This removes some false positives from the uninitialized memory use
detection mechanism.

Fixes #2850.
This commit is contained in:
Andreas Kling 2020-07-27 13:12:17 +02:00
parent f8becd4df8
commit 31b94114c0
3 changed files with 72 additions and 38 deletions
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10
DevTools/UserspaceEmulator/ValueWithShadow.h
View file

@ -59,6 +59,16 @@ public:
return (m_shadow & 0x01) != 0x01;
}
void set_initialized()
{
if constexpr (sizeof(T) == 4)
m_shadow = 0x01010101;
if constexpr (sizeof(T) == 2)
m_shadow = 0x0101;
if constexpr (sizeof(T) == 1)
m_shadow = 0x01;
}
private:
T m_value;
T m_shadow;